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“We continue making improvements with each [carbon dioxide] system and believe that advancing CO2 technologies in supermarket refrigeration systems is absolutely vital."
— Paul Anderson, engineering group manager, Target
PHOENIX — U.S. food retailers testing commercial refrigeration systems that use carbon dioxide as a key refrigerant have found them to have a much smaller impact on climate change — but still carry higher energy and equipment costs — than a traditional refrigeration system.
On the other hand, Sobeys, Stellarton, Nova Scotia, has been rapidly deploying a CO2 system, not yet used in the U.S., that is proving to be financially viable in addition to being environmentally friendly.
Minneapolis-based Target Corp. has experienced an increase in energy use, capital investment and maintenance costs associated with CO2 systems it has tested in two markets compared to a traditional DX (direct expansion) system using R-404A refrigerant, said Paul Anderson, engineering group manager for Target, during a session last month at the Food Marketing Institute’s Energy & Store Development Conference here. However, the test systems had no effect on uptime — which determines a store’s ability to merchandise product — and demonstrated a much lower carbon impact.
“We continue making improvements with each [CO2] system and believe that advancing CO2 technologies in supermarket refrigeration systems is absolutely vital,” Anderson said. “But in order to make this happen, the industry must work together. We need to develop and deliver solutions that reduce the barriers that exist today. We cannot sacrifice energy efficiency improvements.”
Representatives from Fresh & Easy Neighborhood Market, El Segundo, Calif., and Sobeys also described their experiences with CO2 systems at the conference session.
Retailers are exploring refrigeration systems that incorporate CO2 and other “natural” refrigerants such as ammonia in order to reduce the amount of synthetic refrigerants they use, or eliminate them altogether. The latter include R-22, an ozone-depleting gas that is being phased out by the Environmental Protection Agency, and refrigerants such as R-404A, an HFC (hydrofluorocarbon) gas that leaves the ozone layer untouched but contributes significantly to global warming. R-404A, for example has a Global Warming Potential (GWP) of 3,922, compared to a GWP of 1 for CO2; thus, a leak of 1 pound of R-404A would have the same warming effect in the atmosphere as a leak of 3,922 pounds of CO2.
While retailers are being forced to look at alternatives to R-22, they are not expected to replace R-404A or other HFC refrigerants at this time. However, that could change — the Montreal Protocol international agreement on ozone-depleting gases could expand to include HFCs, for example — and the prospect of government regulation of HFC is one reason why systems that use natural refrigerants, which would effectively be immune from regulation, are being considered.
Carbon dioxide systems have other advantages as well. The gas costs between $1 and $2 per pound, compared to $8 to $10 per pound for HFCs, noted Abtar Singh, chief executive officer, Singh360, Maple Grove, Minn., who also spoke at the CO2 session with Anderson. He pointed out that the chemical properties of CO2 mean than “much less CO2 [than R-404A] is needed to get the same cooling effect.” CO2 is also non-toxic, non-flammable and odorless. He expects the energy and maintenance costs of CO2 systems to come down over time.
On the other hand, CO2, particularly when it is the only refrigerant used, sometimes operates at relatively high pressures, though that is generally not considered a major drawback by many industry sources. As a result, CO2 refrigeration systems are somewhat more complex than traditional systems.
Carbon dioxide refrigeration systems usually come in three varieties: One uses CO2 as a “secondary” refrigerant that does the cooling work in the store; another is the “cascade” system in which CO2 has its own compressors; and the third is the “transcritical” system that employs only CO2 — the other two still rely on some amount of a “primary” refrigerant, normally an HFC gas. In the U.S., about 75 CO2 systems — either secondary or cascade — have been installed, while in Canada, Sobeys has deployed 34 transcritical systems, which are more efficient in cooler climates.
“There’s a growing interest in CO2-based refrigeration systems in North America,” said Singh, adding that in Europe, more than 1,500 transcritical and cascade systems have already been installed.